Add sketch file to repo

[kristinashu]

Once we have a few styles and components in our sketch file, we should add it to this repo.

cc @sabrinang @taisdesouzalessa

[kristinashu]

We can add this folder link to the Readme file:
https://drive.google.com/drive/folders/0B2irLVDJivhLY09mcTlFWWhPMVk?usp=sharing
The folder is in: Google Drive / Design Assets / UI Toolkit / Shared Toolkit / [latest sketch file]

It allows anyone with the link to view/download the Sketch file. We will have to make sure the file in that folder is the most recent and we are all working off of it.

@taisdesouzalessa can you please add the Craft Library when you have it?

Eventually, we can add instructions and guidelines.

[taisdesouzalessa]

Here are the instructions on how to install Craft and import our Library:
https://docs.google.com/a/mozilla.com/document/d/1RII8kKpbTh-Ysa-Fg2Xq3Nb1IMgoMjVBdQcAEXGHie8/edit?usp=sharing

The library is at very early stage and we are discussing and agreeing in items to add as we go - items that we have there are not finalized.

Here are the library items:
https://drive.google.com/drive/folders/0B3b1KWRwjxtodENrV2NSVnNlRDA?usp=sharing